1. Field of the Invention
This invention relates to a method for manufacturing a semiconductor device adopting an element isolation structure.
2. Description of the Related Art
An SOI (Silicon On Insulator) structure is conventionally known as an element isolation structure. FIGS. 4A to 4F show a process for manufacturing a semiconductor device in which element isolation is achieved by an SOI structure, and the method for manufacturing this semiconductor device is explained below.
First, as shown in FIG. 4A, oxide films 13a, 13b are respectively formed, by surface oxidation, on a support wafer 11 and a wafer 12 for element formation (element formation wafer) each of which is composed of a silicon wafer. After that, the surfaces of the oxide films 13a, 13b are bonded together, and accordingly, an SOI substrate shown in FIG. 4B is formed, in which the support wafer 11 and the element formation wafer 12 are bonded together with an oxide film 13 interposed between them.
Successively, as shown in FIG. 4C, the element formation wafer 12 is mechanically polished until the thickness of the element formation wafer 12 falls in a range of several xcexc m to about 20 xcexcm, and mirror finishing is performed. Then, as shown in FIG. 4D, trenches 14 are formed such that the trenches 14 extend from the surface of the element formation wafer 12 to the oxide film 13. Element isolation is performed by filling the trenches 14 with an oxide film or poly silicon.
After that, elements (not shown) are formed in respective regions that are isolated from one another, and as shown in FIG. 4E, the SOI substrate is divided into chips. Then, as shown in FIG. 4F, for example, a chip is die-mounted on a substrate 17 such as a metallic plate through conductive paste 16. Thus, a semiconductor device that has isolated elements due to the SOI structure is finished. In this constitution, however, because the bonding wafer having the support wafer 11 is necessitated, the cost is high because of the number of processes required.
The present invention has been made in view of the above problems. An object of the present invention is to simplify a method for manufacturing a semiconductor device having an element isolation structure.
According to the present invention, briefly, after a trench is formed in a wafer from a principal surface of the wafer, the trench is filled with an insulating film. Then, the thickness of the wafer is thinned from a back surface of the wafer so that the insulating film is exposed on the back surface. Accordingly, element isolation of the wafer can be achieved by the insulating film penetrating the wafer from the principal surface to the back surface. It is not necessary to use a bonding wafer. As a result, the method for manufacturing the semiconductor device can be simplified.